1. Technical Field
The present invention relates to a vehicle physical quantity estimating device, and to a memory medium storing a computer program for operating such a device. In particular, the present invention relates to a device for estimating, as vehicle physical quantities, such as, an attitude angle of a vehicle relative to a vertical axis, and/or a vehicle velocity in the forward-reverse (longitudinal) direction and a vehicle velocity in the lateral direction, and to a memory medium storing a computer program for operating such a device.
2. Related Art
The relationship between the acceleration and angular velocity of a rigid moving body and the attitude angle of a vehicle expressed in Euler angles is known from “Introduction to Aircraft Dynamics” (page 12, by Kato, Oya, and Karasawa; published by Tokyo University Publishers, 1982) and the like, and by integration computation based on this relationship, the attitude angle of a vehicle may be derived. However, in simple integration computation, sensor drift errors accumulate, and an accurate attitude angle cannot be derived. In order to overcome such an accumulated error in integration computation, it is necessary to configure an observer that compares the result to the output from another sensor signal and carries out correction so that they approximately match.
As conventional technology using such a correction method for estimating an attitude angle from a vehicle acceleration signal, and angular velocity signal, is the known technology of: using a signal showing vehicle velocity as the another sensor signal, and estimating the sensor inclination angle, that is to say the pitch angle, from the relationship between vehicle velocity, and the longitudinal acceleration and gravitational acceleration (see Japanese Patent Application Laid-Open (JP-A) No. 2002-243494). In this technology, pitch angle is estimated under the presumption that deviations between the value of the integral of vehicle velocity and the value of the longitudinal acceleration arise according to the pitch angle.
Further, as conventional technology for estimating vehicle body slip angle corresponding to vehicle body lateral velocity is the known method of: deriving a difference by subtracting the lateral velocity from the product of the vehicle velocity and the yaw angular velocity, further taking as an estimate value of the cant the sum of this difference and the rate of change in the estimated lateral velocity computed from a vehicle motion model, and by correcting this cant, with the low frequency components of the estimated value of cant taken as the cant components of the road surface, to give a slip angle estimating method that is not influenced by the cant of the road surface (see Japanese Patent Application Laid-Open (JP-A) No. 8-332934).
However, since the vehicle velocity is an estimate computed from the wheel velocities of each of the wheels detected by wheel velocity sensors provided for each of the vehicle wheels, if during acceleration or deceleration a condition of tire slippage develops then an error in the estimation is generated. Therefore if, based on the technology of the above “Introduction to Aircraft Dynamics” (page 12, by Kato, Oya, and Karasawa; published by Tokyo University Publishers, 1982), estimation computation of the pitch angle is carried out simply from the deviation between the value of the integration of the vehicle velocity and the value of the longitudinal acceleration, then there is a problem that errors in the estimated pitch angle increase when there is tire slip during acceleration or deceleration.
Also, the estimated value of cant is a value that increases with an increase in the vehicle body slip angle when spin is generated. Therefore, in conventional technology of the second Patent Publication above, there is a problem that where spin is generated on a low μ road surface at a slow velocity of occurrence, then since this also influences the low frequency components these are interpreted as components of the road surface cant, with the result that the computation of the vehicle body slip angle is corrected, and spin cannot be estimated.
Also, when there is a road surface cant with frequencies the same as or higher than the preset frequency, then since correction for cant is delayed which leads to an increase in the estimated value of the vehicle body slip, there is the problem that this may be misinterpreted as spin.